Solvent flood secondary recovery method



3,121,460 Patented Feb. 18, 1964 3,121,460 SOLVENT FLOOD SECONDARYRECOVERY METHOD John B. Braunwarth and Le Roy W. Holm, Crystal Lake,111., assignors to The Pure Oil Company, Chicago, 111., a corporation ofOhio No Drawing. Filed June 9, 1960, Ser. No. 34,861 6 Claims. (Cl.166-9) This invention relates to the recovery of petroleum fromsubterranean reservoirs. More particularly, it relates to an improvedprocess for recovering petroleum by means of displacement materialsinjected into the reservoir to displace petroleum and drive it towardsproduclng wells. The displacement materials are driven by the injectionof floodwater.

Various secondary-recovery techniques have been proposed for theproduction of additional quantities of oil from reservoirs which haveundergone primary depletion. These methods involve the injection ofvarious materials into the formation to act upon the petroleum oil anddrive the oil to producing wells from which it may be recovered. Waterhas been found to be an outstanding scavenging agent because it is acheap, abundant, stable liquid having a mobility approximating that ofmost petroleum oils. Conventional water-flooding however, still leavesgreat quantities of oil in the formation when the flood has reached thestage where the ratio of waterto-oil being produced is so great that itis uneconomical to continue production. The prior art has discoveredthat improved recoveries may be obtained if the fluid which displacesthe petroleum oil is miscible therewith. Since all known oil-misciblefluids are too expensive to be left in the reservoir, they must bedisplaced by a scavenging fluid, and water is usually preferred for thispurpose. In order to achieve a smooth transition from oil to oil-solubledisplacing fluid to scavenging Water, it is necessary that theoil-soluble fluid be soluble in the scavenging water. The prior art hasaccordingly suggested the use of various alcohols, ketones, aldehydes,etc., for use as miscible solvents which are injected into the formationprior to the injection of flood-Water. Typical of such prior artprocesses is the patent to Morse, No. 2,742,089. Such processes, whilecapable of giving excellent recoveries in laboratory experiments, havenever been applied to actual petroleum reservoir treatment because thereare in fact very few materials having the necessary solubilitycharacteristics which will permit their use as a single-phase solvent.While a few materials such as amyl alcohol, tertiary butyl alcohol, andmethyl ethyl ketone have been found to give outstanding results inlaboratory secondary-recovery water-flood experiments, these materialsare so expensive and must be used in such large quantities that theprocesses are economically unattractive, despite potential oilrecoveries ranging as high as 90% of the oil in place in the reservoirat the time secondary recovery is undertaken.

It is an object of this invention to provide a method for producingrelatively inexpensive solvents for use in conjunction with awater-flood process to enhance oil recoveries. Another object of thisinvention is to provide a method for producing a pair ofmutually-miscible solvents which may be injected in sequence prior toWaterflood to thereby increase the quantities of oil recoverable. Stillanother object of this invention is to provide an improved process forthe secondary recovery of petroleum. Yet another object of thisinvention is to provide a secondary recovery process by which virtuallyall of the petroleum oil in the reservoir can be produced at reasonablecost.

Briefly, the method of this invention, is directed to the treatment ofcrude oxygenated hydrocarbon products to render these products suitablefor use as miscible solvents in secondary recovery of petroleum. Theinvention is further directed to minipulative steps involving the use ofthe treated crude oxygenated hydrocarbon products.

The prior art teaches processes for economically oxidizinglow-molecular-weight hydrocarbons, or mixtures thereof, to produce amixture comprising various partially oxidized hydrocarbons. Thelow-molecular-weight hydrocarbons are oxidized at temperatures of about200 to 500 C. and pressures of about 100 to 2,500 p.s.i. Known oxidizingagents may be used, such as air, oxygen, or other oxygen-containinggases. Complete descriptions of suitable oxidation techniques are givenin Petroleum Refiner, 35, No. 12, 172 (1956); Industrial and EngineeringChemistry, 26, 267 (1934); and Petroleum Engineer, 27, l3Cl4C (December1955). The oxidation products produced by such processes may varysomewhat depending upon the conditions, catalysts, etc., employed, buttypical product distributions approximate those set out in Table I forthe partial oxidation of pentane, butane, and propane.

The crude oxidation product obtained by oxidizing light hydrocarbons isrelatively inexpensive, but such a product tends to be excessivelysoluble in water and insoluble in oil, which detracts from itsefficiency in secondaryrecovery processes. In accordance with thisinvention, an improved method has been devised for producing highlyeflicient solvents for the secondary recovery of petroleum using crude,mixed, oxygenated hydrocarbon products. The novel process of thisinvention consists of preparing a solvent consisting ofoxygen-containing compounds obtained by oxidizing one or more lighthydrocarbons, treating a portion of this solvent with an esterificationcatalyst, such as a small amount of a strong acid, at esterificationconditions to render the mixture preferentially oil soluble, injecting aquantity of preferentially-oil-soluble mixture into a petroleumreservoir, thereafter injecting a quantity of crude oxygenated mixtureinto said reservoir, and finally driving the sequentially-injectedsolvent banks through the reservoir toward producing wells by theinjection of floodwater. Excellent recoveries of both petroleum and theinjected solvent are thereby obtained. Since the methods for producingoxygen-containing compounds by oxidizing light hydrocarbons are wellknown, the starting material for the process of this invention may beconsidered to be either the raw products of these prior art oxidationmethods or the low-molecular-weight hydrocarbons themselves. Sincelow-molecular-weight hydrocarbons are generally available in largeamounts in oil fields, and since the value of such hydrocarbons at theoil fields is relatively low, it is preferred that these materials beused as the starting materials in the process and that they be convertedto hydrocarbon oxidation mixtures by use of suitable prior artprocesses. The product distribution in the mixtures is similar to thoseset out in Table I, depending upon the proportions of the variouslow-molecular-weight hydrocarbons on the feed stock oxidized. Generally,the most economically attractive feed stock is an unseparated mixture ofC to C hydrocarbons. Mixtures of liquefiable petroleum gases, commonlyreferred to as LPG, are suitable for use in the method of this inventionand are preferred in oil fields where LPG is available in sufficientquantities. It should be understood that the crude product from theoxidation process contains small amounts of unconverted hydrocarbonfeed, water, carbon monoxide, and carbon dioxide, and also containsnitrogen where the oxidizing medium is air. Any normally gaseousproducts, such as nitrogen and carbon monoxide, may be stripped from theproduct and discarded. In one embodiment of the process of thisinvention, the unreacted hydrocarbons are separated and recycled. Inanother embodiment of the process of this invention, the unreactedhydrocarbons are not separated, but are retained in admixture with theoxidation products.

In the preferred embodiment of the method of this invention, a portionof the oxidized product is contacted with a catalytic amount of a strongacid at esterification conditions. In this step, the alcohols present inthe oxidized mixture combine with the acids present to form esters,while the aldehydes tend to polymerize. The resulting esters andaldehyde polymers tend to be preferentially soluble in oil as opposed tothe preferential water solubility of the original oxidized mixture.However, the esterified product and the original raw oxidation productare mutually soluble. It is preferred that any acidity in the esterifiedproduct be neutralized by treatment with a base, such as sodiumhydroxide, to prevent corrosion of piping and well casing, and to avoidpossible plugging of the reservoir by the formation of insoluble saltstherein. Moreover, neutralization of the acid followed by removal of awater phase which forms in the esterified product enhances the oilsolubility of the esterified product. The amount of solvent injectedinto a petroleumcontaining reservoir in accordance with the method ofthis invention depends upon the characteristics of the reservoir and thecrude oil contained therein, but in general it is preferred that 0.5 to15.0% of the total pore volume of the reservoir be the amount chosen. Inaccordance with the preferred method of this invention, 0.5 to of thetotal pore volume of an esterified, neutralized, oxidation product isinjected into the reservoir. Then 0.5 to 15 of the pore volume of crudeoxygenated product is injected into the reservoir. The reservoir is thenflooded by the injection of water, and petroleum oil is produced fromthe producing wells until the waterto-oil ratio at the producing wellsbecomes uneconomically high.

One distinct advantage of the method of this invention is that the oilis displaced from the reservoir without displacing large amounts ofreservoir water. Consequently, the oil-to-water ratio in the fluidspumped from the producing wells is much higher than when prior artprocesses are used, and, when production pumping capacity is limited,more oil can be produced in a given amount of time than could be ifconventional processes were used. Also, the use of this recoverytechnique achieves results superior to those achieved by prior artprocesses because a favorable mobility ratio is maintained between thedriven and driving fluids in the reservoir, and this feature providesmore favorable volumetric contact efficiency in the reservoir.

The following examples demonstrate the method of this invention andprovide a comparison with the processes of the prior art.

EXAMPLE I A Berea sandstone core, one foot long and containing 0.63 porevolume of Dollarhide Devonian crude oil and 0.37 pore volume of water,was flooded with water in conventional fashion. When 0.5 pore volume ofwater had been injected, 45% of the oil in place had been recovered. Nomore oil was recovered during the injection of an other pore volume ofwater.

EXAMPLE II A Berea sandstone core, one foot long and containing 0.63pore volume of Dollarhide Devonian crude oil and 0.37 pore volume ofwater, was flooded with 0.45 pore volume of a synthetic mixture ofoxygen-containing hydrocarbons having the composition defined in Table Ias typical of the products obtained by the partial oxidation of butane.Floodwater was then injected, and when 0.5 pore volume of water waspassed into the core, 49% of the oil initially in place was recovered.This recovery increased to 58% during the injection of another porevolume of water. The oil solubility of the synthetic mixturerepresenting butane oxidation products was tested, and it was determinedthat these products had a solubility of 40% in No. 3 white oil. Similarexperiments were carried out on identical Berea sandstone cores usingsynthetic blends of hydrocarbon oxidation products corresponding to thepentane oxidation blend and propane oxidation blend of Table I. After1.5 pore volumes of water had been injected, oil recoveries were 64% inthe case of the pentane oxidation blend, and 54% in the case of thepropane oxidation blend.

EXAMPLE III Into a ZOO-cc. round-bottom flask, equipped with awater-cooled reflux condenser, were placed cc. of a synthetic mixture ofoxygen-containing hydrocarbons as set forth in Table I for the butaneoxidation blend, 8 cc. of distilled water, and 0.5 cc. (0.8 weightpercent) of concentrated sulfuric acid. The total equivalent of acidpresent was 0.26. After refluxing for 2 hours at 57 C., the total acidequivalent present was 0.15. The material was then 40% soluble in No. 3white oil, indicating substantial increase in solubility. Afterrefluxing for two additional hours, the total equivalent of free acidremaining was 0.12, and the material was 50% soluble in No. 3 white oil.The quantity of distilled water added to the synthetic butane oxidationproducts was equivalent to the water which would have been formed in anactual oxidation. No further treatment of the refluxed material was madeprior to use in the secondaryrecovery experiment. 1

A l-foot Berea standstone core, containing 0.63 pore volume ofDollarhide Devonian crude oil and 0.37 pore volume of water, was floodedusing 0.45 pore volume of the esterified product as an oil-solublesolvent bank ahead of the water flood. When 0.5 pore volume of water wasinjected, 68% of the oil initially in place was recovered; when 1.5 porevolumes of water were injected, 77% of the oil initially in place wasrecovered. These recoveries represent increases of 38% and 33% over therecoveries achieved with the original, raw, oxidized hydrocarbon mixturein Example II.

EXAMPLE IV The experiment of Example 3 was repeated using a syntheticoxidized mixture corresponding to the propane oxidation blend as setforth in Table I. A total oil recovery of 59% of the oil initially inplace was obtained after 0.45 pore volume of the refluxed material wasinjected, followed by 1.5 pore volumes of water.

EXAilIPLE V A 500-cc. synthetic blend of oxygen-containing hydrocarbons,as set forth in Table I for the butane oxidation products, and 15 cc. (7weight percent) of concentrated sulfuric acid were charged into aone-liter flask equipped with a reflux condenser. The total equivalentsof acid present were 1.4.- After refluxing for 4 hours at 57 C., thetotal equivalent of acid present was 0.6. After refluxing for 15additional hours, the total equivalent of free acid remained the same. Asolubility check on this material showed it to be 50% soluble in No. 3white oil. It will be observed that this is the same solubility as thatobtained after refluxing for 4 hours after the addition of 0.8 weightpercent of sulfuric acid, as set forth in Example 3. A 100-cc. portionof this material was made neutral by the addition of 5.84 grams ofsodium hydroxide in cold water. The material was filtered to removesalt, and the water phase was separated. The organic upper phase wasfound to be 60% soluble in No. 3 white oil.

A l-foot Berea sandstone core containing 0.63 pore volume of DollarhideDevonian crude oil was flooded by injecting 0.27 pore volume of theabove material followed by 0.18 pore volume of raw butane oxidationproducts, as defined in Table I, and then injecting 1.5 pore volumes ofwater. After the injection of the first pore volume of water, 80% of theoil initially in place was recovered. After the injection of 1.5 porevolumes of water, 89% of the oil initially in place was recovered.lThese recoveries represented increases of 50% and 27% over therecoveries achieved when 0.45 pore volume of the synthetic oxidizedproduct was followed directly by water, as in Example II, andrepresented increases of 78% and 100% over the recoveries achieved withonly floodwater. They further represented increases of 18% and 16% overthe recoveries achieved when the same total volume of an esterifiedoxidation product mixture only was used, as in Example III.

EXAMPLE VI A l-foot Berea sandstone core containing 0.63 pore volume ofDollarhide Devonian crude oil was flooded by injecting 0.27 pore volumeof a fluid consisting of 25% by volume pentane and 75% by volume of theesterified, neutralized organic material produced in Experiment V. Thetotal oil recovery after the injection of 0.27 pore volume of thisfluid, followed by 0.18 pore volume of raw butane oxidation products (asset forth in Table I) and 1.5 pore volumes of Water, amounted to 91% byWeight of the oil initially in place. The 2575 mixture of pentane andesterified material was determined to be 80% soluble in No. 3 White oil.

It is evident that the oil recoveries achieved in Experiments V and VIare very high. The results of each example are given in Table IIfollowing.

identical conditions may be expected to give oil recoveries slightlyhigher, perhaps 1 or 2% higher, than those obtained in Experiments V andVI. It is evident that the method of this invention permits oilrecoveries of a very high order using as solvents materials which arefar less expensive than the pure chemicals suggested by the prior art,and which may readily be produced from raw materials available in oilfields.

When a crude oxygenated-hydrocarbon mixture: is produced using C to Chydrocarbons as a feed stock, it may be preferred not to separate andrecycle the unconverted hydrocarbon feed, as taught by the prior arthydrocarbon oxidation methods, but to permit the unconverted hydrocarbonto remain in admixture with the oxidation products. The unconvertedhydrocarbon will pass unaltered through the refluxing and neutralizationsteps, and will be present in the injected mixture to increase the oilsolubility of the injected mixture and enhance oil recoveries. Thefailure to remove unconverted hydrocarbons will result in a finalproduct approximating that obtained by the addition of hydrocarbon tothe esterified, neutralized finished product as set out in Example VI.

The method of this invention contemplates an alternative process bywhich the crude oxygenated hydrocarbons may be treated. The crudeoxidation products can be separated into a predominantly oil-solublefraction and a predominantly water-soluble fraction by distillation. Thehigher-boiling fraction is first injected into the reservoir, andfollowed by the lower boiling-fraction. Floodwater is then injected todrive the two miscible solvents through the formation. The quantities ofhigher-boiling and lower-boiling fractions injected may be 0.5 to 15.0pore volume percent. Where the hydrocarbon feed to the oxidation processhas a lower boiling point than the temperature at which the oxidationproducts are fractionated, it is evident that the oil-soluble,unconverted hydrocarbon feed will condense with the lower-boiling,predominantly water-soluble materials, such as methanol. In such a caseit is desirable to remove the unconverted hydrocarbon from thepredominantly water-soluble fraction, and either recycle it through theoxidation step, or add it to the higher-boiling fraction to increase theoil solubility thereof.

TABLE H 011 Recoveries from Berea Sandstone Cares Oil Recovery (Percentof oil in place) Example Number Flooding System Solvent Slug (porevolume) With 0.5 With 1.5

pore volpore volume of umes of water water injected injectedConventional water flood 45 Butane oxidation products followed 49 58 bywater. Estcrified butane oxidation prod- 08 77 ucts followed by water.Estcrified propane oxidation prod- 0.45

ucts followed by water. Esterified butane oxidation prod- 0.27esterlfied -1 ucts, followed by unesterified 80 89 oxidation product,followed by 0.18 not cstcrified 1. water. VI 25/75 pentane andcstcrified butane 0.27 25/75 peutane and esterioxidation product,followed by fied product. 85 91 unesterified oxidation product, 0.18uncsterified oxidized mix- I followed by water. ture.

As a specific example of this alternate method, a synthetic oxygenatedhydrocarbon mixture corresponding to the pentane oxidation blend ofTable I was distilled to produce a fraction boiling above 76 C., and afraction boiling below 76 C. In a secondary-recovery experiment, 0.3pore volume of said higher-boiling fraction and 0.2 pore volume of saidlower-boiling fraction were inperiments V and VI. The use of amylalcohol under jected into a 1-foot Berea sandstone core containing 0.62

pore volume of Dollarhide Devonian Crude oil and 0.38 pore volume ofwater. After the injection of 1.5 pore volumes of water, it wasdetermined that 66% of the oil initially in place had been recovered.

A typical product distribution for a pentaue oxidation blend, distilledto remove the materials boiling below about 65 C., is as follows:

The oxidation products of C to C hydrocarbons are used, and it ispreferred that the volumes of the higherboiling and lower-boilingfractions injected be equal, but since the volumes of the two fractionswill seldom be equal, it may be more convenient to inject the fractionsin the volume ratio at which they exist as produced.

In some cases, it may be desired to add a minor amount, 5 to 40% byvolume, of a low-molecular-weight hydrocarbon to the first fluidinjected, i.e., the predominantly oilsoluble fluid, to further increasethe oil solubility thereof. In such cases, it is preferred that amixture of hydrocarbons having about 4 to 8 carbon atoms per molecule bechosen.

The quantity of acid used as an esterification catalyst in the step ofrefluxing the crude oxygenated products is not critical, but it ispreferred to use 0.5 to 10 weight percent of acid. The period ofrefluxing should be suflicient to substantially increase the oilsolubility of the materials, and is usually about 4 hours. Catalystsother than sulfuric acid which may be used include hydrogen chloride,boron fluoride, and cation-exchange resins.

The embodiments of this invention in which a special property orprivilege is claimed are defined as follows:

1. In the secondary recovery of petroleum from a subterranean reservoirby the injection of water through an input well into said reservoir, andthe recovery of petroleum from said reservoir through a producing well,the improvement comprising injecting prior to the injection of water 0.5to 15.0 percent of the total pore volume of a predominantly oil-solublefluid, and then injecting 0.5 to 15.0 percent of the total pore volumeof a predominantly water-soluble fluid, said water-soluble fluidcomprising partial oxidation products of C to C hydrocarbons, and saidoil-soluble fluid having been produced by refluxing the partialoxidation products of the C C hydrocarbons with a small amount ofsulfuric acid for sufficient time to render the refluxed product mixturesoluble in mineral oil to an extent not less than about 40% by volume.

2. A method according to claim 1 in which said oilsoluble fluid afterrefluxing is further treated by neutralizing any acidity with aqueouscaustic, and separating a water phase and an organic phase from said oilsoluble fluid.

3. A method according to claim 2 in which the amount of sulfuric acidused in the refluxing step is about 0.5 to 10.0 weight percent, and saidoil soluble fluid is refluxed for about 4 hours.

4. A method according to claim 3 in which the oilsoluble fluid consistsessentially of about 5 to 40 percent of hydrocarbons and to percent ofneutralized, refluxed, oxygenated hydrocarbons.

5. In the secondary recovery of petroleum from a subterranean reservoirby the injection of water through an input well into said reservoir andthe recovery of petroleum from said reservoir through a producing well,the improvement comprising injecting prior to the injection of water 0.5to 15.0 percent of the total pore volume of a predominantly oil-solublefluid, and then 0.5 to 15.0 percent of the total pore volume of apredominantly watersoluble fluid, said fluids being produced byfractionating the partial oxidation products of C to C hydrocarbons intoa higher-boiling fraction boiling above about 76 C., and a lower-boilingfraction boiling below about 76 C., and separating unconvertedhydrocarbons from said lower-boiling fraction, said higher-boilingfraction being said oil-soluble fluid, and the remaining portion of saidlowerboiling fraction being said water-soluble fluid.

6. A method according to claim 5 wherein the unconverted hydrocarbons,separated from said lower boiling fractions, are combined with saidhigher boiling fractions to produce said predominantly oil-solublefluid.

References Cited in the file of this patent UNITED STATES PATENTS2,742,089 Morse et al Apr. 17, 1956 2,885,002 Jenks May 5, 19592,891,982 Brown June 23, 1959 2,897,894 Draper et al Aug. 4, 19592,934,487 Whitney Apr. 26, 1960

1. IN THE SECONDARY RECOVERY OF PETROLEUM FROM A SUBTERRANEAN RESERVOIRBY THE INJECTION OF WATER THROUGH AN INPUT WELL INTO SAID RESERVOIR, ANDTHE RECOVERY OF PETROLEUM FROM SAID RESERVOIR THROUGH A PRODUCING WELL,THE IMPROVEMENT COMPRISING INJECTING PRIOR TO THE INJECTION OF WATER 0.5TO 15.0 PERCENT OF THE TOTAL PORE VOLUME OF A PREDOMINANTLY OIL-SOLUBLEFLUID, AND THEN INJECTING 0.5 TO 15.0 PERCENT OF THE TOTAL PORE VOLUMEOF A PREDOMINANTLY WATER-SOLUBLE FLUID, SAID WATER-SOLUBLE FLUIDCOMPRISING PARTIAL OXIDATION PRODUCTS OF C3 TO C8 HYDROCARBONS, AND SAIDOIL-SOLUBLE FLUID HAVING BEEN PRODUCED BY REFLUXING THE PARTIALOXIDATION PRODUCTS OF THE C3-C8 HYDROCARBONS WITH A SMALL AMOUNT OFSULFURIC ACID FOR SUFFICIENT TIME TO RENDER THE REFLUXED PRODUCT MIXTURESOLUBLE IN MINERAL OIL TO AN EXTENT NOT LESS THAN ABOUT 40% BY VOLUME.